WHARF

PROCESSING

Crushing Facility | Leaching | Neutralization | Recovery Plant

Crushing Facility

The crusher is comprised of a 250-ton storage hopper. The run-of-mine gold ore is transferred from the hopper via an apron feeder to a vibrating grizzly where all rock less than 6 inches is separated out. The larger material is sent through a jaw crusher. The jaw crusher product is further screened and crushed with five cone crushers and five screen decks until it reaches the 13⁄2 inch size. Granulated lime is added to the ore during crushing to provide control of the pH in the leach solution during processing.

Leaching

The crushed ore is hauled by the pit operations equipment fleet to one of four on-off heap leach pads and placed in 20-foot lifts to a maximum height of 150 feet over the pad liner.

The four leach pads used for ore processing cover approximately 70 acres with a capacity of 9.0 million tons. The pad design includes double synthetic liners on top of 8 inches of compacted clay, with a leak detection system located between the two synthetic liners.  This system is closely monitored to ensure the integrity of the liners.

A dilute alkaline cyanide solution is distributed through the crushed rock by drip emitters that are installed on the top of each lift. As the solution percolates down through the ore, the gold is leached from the ore and the gold-laden solution gravity flows through pipelines to the processing plant.

The leaching process usually is complete approximately 12 to 18 months after the pad is completely full. The current average gold recovery rate is 74.5%.

Neutralization

Once the pad has been fully leached, the heap is then rinsed with water and neutralized with hydrogen peroxide to oxidize residual cyanides. Nitrates and metals are reduced to regulated levels prior to disposal.

A bio-denitrification process is used to remove nitrate from the neutralization de-nitrifying circuit. In this process, bacteria break down the nitrate into nitrogen gas and oxygen. The bacteria consume the oxygen attached to the nitrate for respiration. The nitrogen gas by-product is vented off to the atmosphere.

Following neutralization, the spent ore is hauled to the Foley spent ore disposal site, which has been specifically approved for depositing spent ore.

Recovery Plant

Through the addition of extra carbon columns the recovery plant now has the capacity to treat 3,800 gallons/minute of pregnant solution. The adsorption circuit consists of 19 carbon columns holding a total of 39 tons of activated carbon where the gold is removed from the solution.

The activated carbon (loaded with gold) is moved to the stripping plant where it enters a closed circuit under high pressure and temperature. Gold is electro plated from the circuit and the precious metal sludge is then shipped to a third party refinery for further processing.